Temperature modulated differential scanning calorimetry. Part III. Effect of heat transfer on phase angle in quasi-isothermal ADSC

The effect of heat transfer on the phase measurements of alternating differ ential scanning calorimetry (ADSC, Mettler-Toledo) has been investigated, c ontinuing previous work, using quasi-isothermal experiments. A new model fo r the prediction of the effects of heat transfer has been suggested in this work, acid more closely simulates the practical conditions than did the ea rlier model. In particular, the reference sensor temperature is compared wi th the sample sensor temperature rather than with the sample temperature it self, as was used in the previous model. Both theoretical simulation and ex perimental results show that, a phase angle is introduced simply by virtue of heat transfer effects, and that it depends on many experimental paramete rs. In particular, it is independent of the amplitude of temperature modula tion, but depends strongly (and non-linearly) on the frequency and approxim ately linearly on the sample mass, To a large extent, these dependencies ar e well predicted by the theoretical model, which also predicts a strong inf luence of the heat transfer coefficient characterising the quality of the i nterface been sample and pan. It is shown that the use of a heat transfer f luid can largely eliminate the inconsistencies in the interfacial contact b etween sample and pan. (C) 1999 Elsevier Science B.V. All rights reserved.